1. Field of the Invention
The present invention relates generally to projection display devices, and more particularly, to an active matrix type projection display device, typically a rear projection type or a front projection type liquid crystal display device.
2. Description of the Related Art
The development of techniques for manufacturing semiconductor devices, such as a thin-film transistor (TFT), having a semiconductor thin film formed on a low-priced glass substrate, has recently been promoted with the increase in demand for active matrix liquid crystal display devices (liquid crystal panels).
Also, projection type liquid crystal display devices (liquid crystal projectors) have attracted attention, in which pixel portions of liquid crystal panels are irradiated with strong light from a light source, and light passed through the pixel portions is projected to a screen through a lens to form an enlarged image which are enjoyed by a viewer.
FIG. 18 is a diagram schematically showing the construction of a conventional three-panel type liquid crystal projector using three liquid crystal panels. Light source 8001 is a white light source. Each of dichroic mirrors 8002, 8003, 8004, and 8005 reflects only light having wavelengths in a certain wavelength region and allows light having wavelengths in the other regions to pass therethrough. The dichroic mirror 8002 reflects only red light and allows light of the other colors to pass therethrough. The dichroic mirrors 8003 and 8004 reflect only blue light and allow light of the other colors to pass therethrough. Further, the dichroic mirror 8005 reflects only green light and allows light of the other colors to pass therethrough. Mirrors 8006 and 8007 are total reflection mirrors. Liquid crystal panels 8008, 8009, and 8010 are provided to display red, blue and green images, respectively.
FIG. 19 shows the principle of a three-panel type projector. As shown in FIG. 19, a three-panel type projector provides a color image by combining red, green, and blue images.
As shown in FIG. 20, a case where a defective pixel 9001 exists in the liquid crystal panel 8010 (normally white) displaying a green image will be described. If the defective pixel 9001 is a bright dot, it is subjected to processing of irradiation with laser light or the like to be changed into a dark dot.
In the case where a defective pixel 9001 exists in the liquid crystal panel 8010 which displays a green image, a defect due to the dark dot appears in the green image. It is assumed here that each of the liquid crystal panel 8008 displaying the red image and the liquid crystal panel 8009 displaying the blue image has no defective pixel. In the color image formed by combining the three color images, due to the defective pixel in the green image the brightness of the pixel is reduced, and the pixel 9002 with the defect has a purplish color image displayed by combining a red image and a blue image.
Therefore, image in this defective portion is perceptible, thus causes deteriorating the quality of the displayed image.